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• 1
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Isobutane pyrolysis has been studied at 20-200 torr initial pressures and 773-793 K, in a packed reactor treated with PbO and in a reactor packed with platinum foils. These packings strongly inhibit product formation and this effect is explained by the occurrence of the heterogeneous termination step:\documentclass{article}\pagestyle{empty}\begin{document}$\rm H\cdot\mathrel{\mathop{\relbar\joinrel\longrightarrow}^{walls}} product$\end{document}at the reactor walls. The reaction has been modeled in the temperature and pressure range on the basis of a kinetic scheme which has been proposed for the homogeneous reaction and step (w) with the following values of kw:\eqalign{(k_{_{w}})_{_{\rm{PbO}}}&=3.7\ 10^{8}\ \rm{exp} \left[-{9000\over \rm{T}}\right]\rm{S}^{-1}\cr(k_{_{w}})_{_{\rm{Pt}}}&=15000\ \rm{S}^{-1}\ \rm{at\ any\ temperature}\cr}for both types of packing. The corresponding sticking coefficients of hydrogen atoms are:\eqalign{\gamma _{_{\rm{PbO}}} &=160\ \rm{exp} \left[-{9000\over \rm{T}}\right]\cr\gamma _{_{\rm{Pt}}} &=0.03\cr}© 1998 John Wiley & Sons, Inc. Int J Chem. Kinet 30: 439-450,1998
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• 2
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: N-cyanomethyl-N-ethyl aniline (CEAN) and N-cyanomethyl-N-ethyl-p-anisidine (CEPA) have been thermolyzed in a stirred-flow reactor, in the range of 510-560 °C, pressures of 7-11 torr and residence times of 0.5-0.9 s, using toluene as carrier gas. N-cyanomethyl-N-ethyl-p-nitroaniline (ECNA) was thermolyzed at 640°C and 13% conversion. Ethylene and HCN formed in 43% yield each as products from all three starting materials. Phenyl methanaldimine and p-anisidyl methanaldimine were also products of CEAN and CEPA, respectively. The consumption of CEAN and CEPA showed first-order kinetics for a three-fold increase of reactant inflow and initial conversions of up to 40 percent. The following Arrhenius equations were obtained from the rate coefficients for the production of ethylene: CEAN: k=1015.10±0.74 exp(-238±11 kJ/mol·RT); CEPA: k=1015.61±0.29 exp(-246±4 kJ/mol·RT). The results are explained by means of radical, nonchain thermolysis mechanisms. The thermochemistry of relevant reaction steps has been estimated from thermochemical parameters calculated by using the semiempirical AM1 method. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 451-456, 1998
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• 3
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A (s-1) and Ea (kJ mol-1) of the analogues (1-5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(\documentclass{article}\pagestyle{empty}\begin{document}$\underline{\rm{p}}$\end{document}-nitrophenylhydrazono)-propanone (2) , 10.68 and 144.9 for 1-cyano-1-(\documentclass{article}\pagestyle{empty}\begin{document}$\underline{\rm{p}}$\end{document}-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 s-1 and 143.3 kJ mol-1. The rates of reaction at 600 K are compared with those of the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 457-462, 1998
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• 4
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Solvent effects on the kinetics of hydrolysis of isatin by sodium hydroxide have been investigated within the temperature range (30-55°C) in methanol-water and acetonitrile-water media of varying solvent compositions up to 70% (v/v) of the organic solvent component. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions; log k was correlated with both log [H2O] and the reciprocal of the dielectric constant. The first correlation was observed to be linear while the second was nonlinear. Finally a mechanism for the isatin ring opening was proposed, which accounts for the role and the effect of the solvent on the reaction rate. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 463-469, 1998
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• 5
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with the dibasic esters dimethyl succinate [CH3OC(O)CH2CH2C(O)OCH3], dimethyl glutarate [CH3OC(O)CH2CH2CH2C(O)OCH3], and dimethyl adipate [CH3OC(O)CH2CH2CH2CH2C(O)OCH3] at 298±3 K. The rate constants obtained were (in units of 10-12 cm3 molecule-1 s-1): dimethyl succinate, 1.4±0.6; dimethyl glutarate, 3.3±1.1; and dimethyl adipate, 8.4±2.5, where the indicated errors include the estimated overall uncertainty of ±25% in the rate constant for cyclohexane, the reference compound. The calculated tropospheric lifetimes of these dibasic esters due to gas-phase reaction with the OH radical range from 1.4 days for dimethyl adipate to 8.3 days for dimethyl succinate for a 24 h average OH radical concentration of 1.0×106 molecule cm-3. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 471-474, 1998
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• 6
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Photolysis of S2O8= in strong alkaline solutions (pH 〉 13) in the presence of molecular oxygen yields ozonide radical ions, \documentclass{article}\pagestyle{empty}\begin{document}$\rm{O^{\textstyle{\cdot}-}_{3}}$\end{document}. These radicals show a complex decay rate sensitive to the peroxodisulfate concentration. A reaction mechanism, which includes the reaction of O•- and S2O8= with a rate constant k=(3-6)×106M-1s-1 and accounts for the experimental results is discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 491-496, 1998
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• 7
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Pulse radiolysis was used to study the kinetics of the reactions of CH3C(O)CH2O2 radicals with NO and NO2 at 295 K. By monitoring the rate of formation and decay of NO2 using its absorption at 400 and 450 nm the rate constants k(CH3C(O)CH2O2+NO)=(8±2)×10-12 and k(CH3C(O)CH2O2+NO2)=(6.4±0.6)×10-12 cm3 molecule-1 s-1 were determined. Long path length Fourier transform infrared spectrometers were used to investigate the IR spectrum and thermal stability of the peroxynitrate, CH3C(O)CH2O2NO2. A value of k-6≈3 s-1 was determined for the rate of thermal decomposition of CH3C(O)CH2O2NO2 in 700 torr total pressure of O2 diluent at 295 K. When combined with lower temperature studies (250-275 K) a decomposition rate of k-6=1.9×1016 exp (-10830/T) s-1 is determined. Density functional theory was used to calculate the IR spectrum of CH3C(O)CH2O2NO2. Finally, the rate constants for reactions of the CH3C(O)CH2 radical with NO and NO2 were determined to be k(CH3C(O)CH2+NO)=(2.6±0.3)×10-11 and k(CH3C(O)CH2+NO2)=(1.6±0.4)×10-11 cm3 molecule-1 s-1. The results are discussed in the context of the atmospheric chemistry of acetone and the long range atmospheric transport of NOx. © John Wiley & Sons, Inc. Int J Chem Kinet: 30: 475-489, 1998
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• 8
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The room temperature rate coefficient for the reaction Br+Br2O→Br2+BrO (3) has been measured using the technique of pulse-laser photolysis with long-path transient absorption detection of the BrO reaction product. A value of k3=(2.0±0.5)×10-10 cm3 molecule-1 s-1 was determined. The photolysis products of Br2O at 308 nm were also examined. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 571-576, 1998
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• 9
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Tert-Butyl hydroperoxide and hydrogen peroxide readily react with the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The reaction is inhibited by ABTS and protons, and can be interpreted in terms of a mechanism comprising a partially reversible electron transferROOH+ABTS•+↔ ROO · + ABTS + H+ (1)followed by the self-reactions of the hydroperoxide derived radicals and reactions between them and another ABTS derived radical. A complete kinetic analysis allows an evaluation of the rate constant for reaction (1). A value of 0.2 M-1 s-1 was obtained for both compounds. The back reaction of process (1) is more relevant when tert-butyl hydroperoxide is employed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 565-570, 1998
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• 10
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO have been investigated at room temperature and 740 torr total pressure of air by gas chromatography with flame ionization detection, in situ Fourier transform infrared absorption spectroscopy, and direct air sampling atmospheric pressure ionization tandem mass spectrometry. The products identified and quantified by GC-FID and in situ FT-IR absorption spectroscopy were HCHO, 2-methylpropanal, acetone, glycolaldehyde, and methacrolein, with formation yields of 0.70±0.06, 0.58±0.08, 0.17±0.02, 0.18±0.03, and 0.033±0.007, respectively. In addition, IR absorption bands due to organic nitrates were observed, consistent with API-MS observations of product ion peaks attributed to the β-hydroxynitrates (CH3)2CHCH(ONO2)CH2OH and/or (CH3)2CHCH(OH)CH2ONO2 formed from the reactions of the corresponding β-hydroxyalkyl peroxy radicals with NO. A formation yield of ca. 0.15 for these nitrates was estimated using IR absorption band intensities for known organic nitrates. These products account for essentially all of the reacted 3-methyl-1-butene. Analysis of the potential reaction pathways involved shows that H-atom abstraction from the allylic C(SINGLEBOND)H bond in 3-methyl-1-butene is a minor pathway which accounts for 5-10% of the overall OH radical reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 577-587, 1998
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• 11
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO3 radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: kOH=(3.9±1.2)×10-11 cm3 molecule-1 s-1, kO3=(8.6±2.9)×10-18 cm3 molecule-1 s-1, kNO3=(8.6±2.9)×10-15 cm3 molecule-1 s-1, and kCl=(4.7±1.0)×10-10 cm3 molecule-1 s-1. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O3, NO3, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589-594, 1998
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• 12
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The apparent rate constants of formation (k1) and hydrolysis (k2) of the Schiff bases formed between pyridoxal and polyallylamine has been fitted to a kinetic scheme that involve the different protonated species in the reaction medium and the individual rate constants of formation (k1i) and hydrolysis (k2i). The (k1i) values precludes an acid catalyzed intramolecular process. The effects of hydrophobic medium due to the presence of the macromolecule on the reaction is also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 1-6, 1998.
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• 13
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Upper limits of 4×10-20 and 7×10-20 cm3 molecule-1 s-1 were established for the gas-phase reactions of H2O2 with O3 and NO, respectively. These reactions are too slow to explain features observed in the atmospheric vertical profile of H2O2. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 707-709, 1998
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• 14
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The pulse-radiolysis technique has been employed to produce and study the kinetics of hydrated electrons (eaq-) in a quaternary micro emulsion (Sodium Lauryl Sulfate (NaLS)/water/cyclohexane/1-pentanol) system. Two orders of magnitude higher life time (20 μs) of the eaq- has been obtained as compared to that in reverse micelles reported earlier. Several probes including a biomolecule have been used to determine the water pool concentrations and quenching constants (kq). The observed yield and half life (t1/2) of the hydrated electrons vary smoothly as the water droplet sizes are changed. The bimolecular rate constants for the reaction of eaq- with different solutes have been determined. It has been observed that the measured bimolecular rate constants for the reaction of hydrated electrons with different solutes are indicative of the solubilization sites, the water core sizes, and the surrounding environment. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 699-705, 1998
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• 15
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The photochemistry of IrCl62- complex in simple alcohols have been studied using laser-flash photolysis. Single electron transfer from the solvent molecule to the light-excited complex has been shown to be the primary photochemical process. Quantum yields of the photoreduction of IrCl62- complex and the rate constants of its reaction with hydroxyalkyl radicals were determined at 200-330 K. Deviations of the rate constants from Debye-Smoluchowski equation for diffusion-controlled reactions are discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 711-719, 1998
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• 16
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate coefficients for the reactions of hydrogen atoms with n-C3H7Br, s-C3H7Br, n-C4H9Br, and s-C4H9Br were determined in a discharge flow-reactor at 298 K and a pressure of 4 mbar. Molecular-beam sampling and subsequent mass-spectrometric detection with electron-impact ionisation was used for the measurement of the bromo-hydrocarbon concentration. The rate coefficients obtained are (in 1010 cm3 mol-1 s-1): 2.3±1.2 for n-C3H7Br, 2.3±1.2 for s-C3H7Br, 2.4±1.2 for n-C4H9Br, and 2.8±1.4 for s-C4H9Br. The results are compared with predictions from bond-energy bond-order (BEBO) calculations, where a reasonable agreement is found. Furthermore, also by BEBO calculations, the relative importance of bromine abstraction as compared to hydrogen abstraction is estimated. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 721-727, 1998
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Potential-energy surfaces for various channels of the HNO+NO2 reaction have been studied at the G2M(RCC,MP2) level. The calculations show that direct hydrogen abstraction leading to the NO+cis-HONO products should be the most significant reaction mechanism. Based on TST calculations of the rate constant, this channel is predicted to have an activation energy of 6-7 kcal/mol and an A factor of ca. 10-11 cm3 molecule-1 s-1 at ambient temperature. Direct H-abstraction giving NO+trans-HONO has a high barrier on PES and the formation of trans-HONO would rather occur by the addition/1,3-H shift mechanism via the HN(O)NO2 intermediate or by the secondary isomerization of cis-HONO. The formation of NO+HNO2 can take place by direct hydrogen transfer with the barrier of ca. 3 kcal/mol higher than that for the NO+cis-HONO channel. The formation of HNO2 by oxygen abstraction is predicted to be the least significant reaction channel. The rate constant calculated in the temperature range 300-5000 K for the lowest energy path producing NO+cis-HONO gave rise to\documentclass{article}\pagestyle{empty}\begin{document}$k_{a}=7.34\cdot 10^{-20}\ \rm{T}^{2.64}\ \rm{exp}(-2034/T)\ \rm{cm}^{3}\ \rm{molecule}^{-1}\ \rm{s}^{-1}.$\end{document}© 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 729-736, 1998
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• 18
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of +2-butanol (2BU, CH3CH2CH(OH)CH3) and 2-pentanol (2PE, CH3CH2CH2CH(OH)CH3). 2BU and 2PE react with OH yielding bimolecular rate constants of (8.1±2.0)×10-12 cm3molecule-1s-1 and (11.9±3.0)×10-12 cm3molecule-1s-1, respectively, at 297±3 K and 1 atmosphere total pressure. Both 2BU and 2PE OH rate constants reported here are in agreement with previously reported values [1-4]. In order to more clearly define these alcohols' atmospheric reaction mechanisms, an investigation into the OH+alcohol reaction products was also conducted. The OH+2BU reaction products and yields observed were: methyl ethyl ketone (MEK, (60±2)%, CH3CH2C((DOUBLEBOND)O)CH3) and acetaldehyde ((29±4)% HC((DOUBLEBOND)O)CH3). The OH+2PE reaction products and yields observed were: 2-pentanone (2PO, (41±4)%, CH3C((DOUBLEBOND)O)CH2CH2CH3), propionaldehyde ((14±2)% HC((DOUBLEBOND)O)CH2CH3), and acetaldehyde ((40±4)%, HC((DOUBLEBOND)O)CH3). The alcohols' reaction mechanisms are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. Labeled (18O) 2BU/OH reactions were conducted to investigate 2BU's atmospheric transformation mechanism details. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground level ozone-forming potential calculations (incremental reactivity) [5]. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 745-752, 1998
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The influence of the mass transfer phenomena on the thermal decomposition of calcium carbonate powders under vacuum was investigated through a detailed kinetic analysis by the constant transformation rate thermal analysis (CRTA). Reliable kinetic curves, free from the mass transfer problems, can be obtained by CRTA under vacuum, but within a restricted range of small sample sizes, 〈10 mg. The influence of mass transfer phenomena on the apparent kinetic parameters is discussed in relation to the distribution of fractional reaction α of the individual particles in a sample assemblage. Only when the distribution of α is maintained constant among a series of experimental kinetic curves, can a reliable activation energy, E, be obtained by one of the isoconversion methods. In this respect, a single cyclic CRTA permits the α distribution to be maintained constant between the two adjacent data points with different decomposition rates. In the present study, an apparent E value of about 223 kJ mol-1 was obtained by the Friedman method from a series of CRTA curves with sample sizes less than 10 mg and by the rate jump method from a single cyclic CRTA curve with sample size of about 40 mg. The first-order (F1) law was determined to be the most appropriate kinetic model function, from a series of CRTA curves, instead of the ideal contracting geometry (R3) law formalized for the three-dimensional shrinkage of the reaction interface in the respective particles. The particle size distribution of the sample particles is suggested to be one possible reason for the apparent agreement with the F1 law. A kinetic exponent n of the nth-order law that deviated from unity was obtained from the CRTA curves with sample sizes larger than 10 mg, due to an additional distribution of α produced by mass transfer phenomena. Because the α distribution due to the mass and heat transfer phenomena cannot be expressed practically in an analytical function, a meaningful kinetic model and preexponential factor are difficult to estimate from kinetic data that are influenced by the transfer phenomena. © 1998 John Wiley & Sons, Inc. Int. J Chem Kinet: 30: 737-744, 1998
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Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction of 2-phenoxyquinoxaline (1) with hydroxide ion is accelerated by reactive counter-ion micelles of cetyltrialkylammonium hydroxides (alkyl=Me, Et, n-Pr, and n-Bu), cetylmethylpiperidinium hydroxide, and cetylquinuclidinium hydroxide containing bulky head groups. First-order rate constants for reaction of (1) with OH- increase with increasing bulk of the head group and are associated with an increase in nucleophile reactivity as water is squeezed away from the micelle surface. Micellar effects upon the alkaline hydrolysis of compound (1) were analyzed by using a model that describes micelle-ion interactions in terms of Langmuir isotherms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 777-783, 1998
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Ab initio calculations have been used to characterize the transition states for halogen abstraction by CH3 in reactions with CF4, CF3Cl, CF3Br, and CF3I (1-4). Geometries and frequencies were obtained at the HF/6-31G(d) and MP2=full/6-31G(d) levels of theory. Energy barriers were computed via the Gaussian-2 methodology, and the results were employed in transition state theory analyses to obtain the rate constants over 298-2500 K. There is good accord with literature measurements in the approximate temperature range 360-500 K for reactions (2-4), and the computed activation energies are accurate to within ±6 kJ mol-1. Recommended rate constant expressions for use in combustion modeling are k;1=1.6×10-19 (T/K)2.41 exp(-13150 K/T), k2=8.4×10-20(T/K)2.34 exp(-5000 K/T), k3=4.6×10-19 (T/K)2.05 exp(-3990 K/T), and k4=8.3×10-19 (T/K)2.18 exp(-1870 K/T) cm3 molecule-1 s-1. The results are discussed in the context of flame suppression chemistry. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 179-184, 1998.
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Source: Wiley InterScience Backfile Collection 1832-2000
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Notes: Manganese(II) is oxidized by ozone in acid solution, k=(1.5±0.2)×103 M-1 s-1 in HClO4 and k=(1.8±0.2)×103M-1 s-1 in H2SO4. The plausible mechanism is an oxygen atom transfer from O3 to Mn2+ producing the manganyl ion MnO2+, which subsequently reacts rapidly with Mn2+ to form Mn(III). No free OH radicals are involved in the mechanism. The spectrum of Mn(III) was obtained in the wave length range 200-310 nm. The activation energy for the initial reaction is 39.5 kJ/mol. Manganese(III) is reduced by hydrogen peroxide to Mn(II) with k(Mn(III)+H2O2)=2.8×103M-1 s-1 at pH 0-2. The mechanism of the reaction involving formation of the manganese(II)-superoxide complex and reaction of H2O2 with Mn(IV) species formed due to reversible disproportionation of Mn(III), is suggested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 207-214, 1998.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Using stationary-point information from a BAC-MP4 potential-energy surface and statistical-dynamical methods, we have calculated the total rate coefficient for the two-channel reaction,\documentclass{article}\pagestyle{empty}\begin{document}$CH3+NO\rightarrow HCN+H2O\quad (R1)$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$\rightarrow H2CN+OH,\quad (R2)$\end{document}in the temperature range 1000 K≥T≥2500 K. The result obtained,\documentclass{article}\pagestyle{empty}\begin{document}$kT=3.0 \times 10-1T3.52exp(-3950/RT) cm3/mole s,$\end{document}is in excellent agreement with recent shock-tube measurements of kT by Braun-Unkhoff, et al. and Hennig and Wagner. Qualitative considerations suggest that the radical channel (R2) is dominant in this temperature range. The analysis and the results are discussed in some detail. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 223-228, 1998.
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• 24
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Notes: The reduction of iodine by hydroxylamine within the [H+] range 3×10-1-3×10-4 mol.L-1 was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH3OH+]0/[I2]0 ratio below 15, [H+] around 0.1 mol.L-1, and ionic strength around 0.1 mol.L-1), the [I2] and [I3-] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I2+I-⇔I3-, 2 I2+NH3OH++H2O→HNO2+4 I-+5 H+, NH3OH++HNO2→N2O+2 H2O+H+, and 2 HNO2+2 I-+2 H+→2 NO+I2+2 H2O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h).The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H+] is above 4×10-2 mol.L-1 at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH2OH and NH3OH+ as the reducing reactive species. The additional rate suppression by H+ at low pH would be connected to the existence of H2OI+ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785-797, 1998
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Notes: Collisional deactivation of I(2P1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH3Cl, CH2Cl2, CHCl3, CCl3F, and CCl4 are 3.1±0.3×10-13, 1.28±0.08×10-13, 5.7±0.3×10-14, 3.9±0.4×10-15, and 2.3±0.3×10-15cm3 molecule-1 s-1, respectively, at room temperature (298 K).The higher efficiency observed for relaxation by CH3Cl, CH2Cl2, and CHCl3 reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm-1) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799-803, 1998
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Notes: A comprehensive detailed chemical kinetic mechanism for methanol oxidation has been developed and validated against multiple experimental data sets. The data are from static-reactor, flow-reactor, shock-tube, and laminar-flame experiments, and cover conditions of temperature from 633-2050 K, pressure from 0.26-20 atm, and equivalence ratio from 0.05-2.6. Methanol oxidation is found to be highly sensitive to the kinetics of the hydroperoxyl radical through a chain-branching reaction sequence involving hydrogen peroxide at low temperatures, and a chain-terminating path at high temperatures. The sensitivity persists at unusually high temperatures due to the fast reaction of CH2OH+O2=CH2O+HO2 compared to CH2OH+M=CH2O+H+M. The branching ratio of CH3OH+OH=CH2OH/CH3O+H2O was found to be a more important parameter under the higher temperature conditions, due to the rate-controlling nature of the branching reaction of the H-atom formed through CH3O thermal decomposition. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 805-830, 1998
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Notes: The aminolysis reactions of O-ethyl S-(Z-phenyl) dithiocarbonates (Z=p-CH3, H, p-Cl, and p-NO2) with anilines (AN) and N,N-dimethylanilines (DMA) in acetonitrile at 30.0°C are investigated. Relatively small values of βX (βnuc,0.4 ca. 0.7) and βZ (βlg -0.1 ca. -0.4) for both ANs and DMAs, significantly large kH/kD values (1.1 ca. 1.9) involving deuterated anilines, and large negative ρXZ values for ANs (-0.56) are interpreted to indicate a concerted mechanism for both ANs and DMAs but with a hydrogen bonded four-center type transition state (TS) for ANs. The relative leaving ability, k(Z=p-NO2)/k(Z=p-CH3), is smaller for ANs than for DMAs, especially for a weaker nucleophile (1.9 and 4.7 for AN and DMA, respectively, with X=p-Cl). This suggests that the rate enhancement by the hydrogen-bond formation in the four-center type TS for AN is greater for a weaker nucleofuge (Z=p-CH3), especially when the nucleophile (X=p-Cl) is weaker. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 419-423,1998
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Notes: Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20-100 torr initial pressures and 750-793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self-inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425-437, 1998
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Notes: The gas-phase reaction of bornyl acetate (bicyclo[2,2,1]-heptan-2-ol-1,7,7-trimethyl-acetate) with hydroxyl radical has been studied. A relative method was used to determine the rate constant for this reaction, with n-octane as reference compound.Methyl nitrite photolysis experiments were carried out in an environmental smog chamber at atmospheric pressure and (294±2) K. The rate constant determined for bornyl acetate is k=(13.9±2.2)×10-12 cm3 molecule-1 s-1.The experimental rate constant has been compared with the rate constants calculated with the structure-activity relationship (SAR) and with the evolution trend of the acetate rate constants. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 497-502, 1998
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Notes: The thermal reaction of propene was examined around 800 K in the presence of less than 20% oxygen. At initial time, the production of H2, CH4, C2H4, C2H6, allene, C3H8, 1,3-butadiene, butenes, 3- and 4-methylcyclopentene, a mixture of 1,4- and 1,5-hexadienes, methylcyclopentane (or dimethylcyclobutane), 4-methylpent-1-ene, and hex-1-ene, was observed along with hydrogen peroxide, CO, and small quantities of ethanal and CO2. Oxygen increases the initial production of hydrogen and of most hydrocarbons and, particularly, that of C6 dienes and of cyclenes. However, the production of allene, methylcyclopentane (or dimethylcyclobutane), and 4-methylpent-1-ene is practically not affected. A kinetic study confirms the mechanism proposed for the thermal reaction of propene. Formation of allene, thus, involves a four-center-unimolecular dehydrogenation of propene, that of 4-methylpent-1-ene is explained by an ene bimolecular reaction while methylcyclopentane (or dimethylcyclobutane) probably arises from a bimolecular process involving a biradical intermediate. Other products arise from a conventional chain radical mechanism.A kinetic scheme is proposed in which chains are primarily initiated by the bimolecular step:C3H6+O2→HO2·+C3H5·which competes with the second-order initiation of propene pyrolysis. Since allene production is not affected by oxygen, it is concluded that allyl radicals are not dehydrogenated by oxygen; but they oxidize in a branching step involving allylperoxyl radicals; r. radicals other than methyl, and allyl are dehydrogenated according to the conventional process:r·+O2→unsaturated+HO2·and account for the production of a large excess of C6 diolefins, methylcyclopentenes, and hydrogen peroxide, when r. stands for C6H11, the allyl adduct. Hydrogen peroxide gives rise to a degenerate branching of chains. Based on the proposed scheme, a modeling of the reaction is shown to account fairly well for the concentration-time profiles. Rate constants of many steps are evaluated and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 503-522, 1998
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Notes: Ligand substitution kinetics for the reaction [PtIVMe3(X)(NN)]+NaY=[PtIVMe3(Y)(NN)]+NaX, where NN=bipy or phen, X=MeO-, CH3COO-, or HCOO-, and Y=SCN- or N3-, has been studied in methanol at various temperatures. The kinetic parameters for the reaction are as follows. The reaction of [PtMe3(OMe)(phen)] with NaSCN: k1=36.1±10.0 s-1; ΔH1≠=65.9±14.2 kJ mol-1; ΔS1≠=6±47 J mol-1 K-1; k-2=0.0355±0.0034 s-1; ΔH-2≠=63.8±1.1 kJ mol-1; ΔS-2≠=-58.8±3.6 J mol-1 K-1; and k-1/k2=148±19. The reaction of [PtMe3(OAc)(bipy)] with NaN3: k1=26.2±0.1 s-1; ΔH1≠=60.5±6.6 kJ mol-1; ΔS1≠=-14±22 J mol-1K-1; k-2=0.134±0.081 s-1; ΔH-2≠=74.1±24.3 kJ mol-1; ΔS-2≠=-10±82 J mol-1K-1; and k-1/k2=0.479±0.012. The reaction of [PtMe3(OAc)(bipy)] with NaSCN: k1=26.4±0.3 s-1; ΔH1≠=59.6±6.7 kJ mol-1; ΔS1≠=-17±23 J mol-1K-1; k-2=0.174±0.200 s-1; ΔH-2≠=62.7±10.3 kJ mol-1; ΔS-2≠=-48±35 J mol-1K-1; and k-1/k2=1.01±0.08. The reaction of [PtMe3(OOCH)(bipy)] with NaN3: k1=36.8±0.3 s-1; ΔH1≠=66.4±4.7 kJ mol-1; ΔS1≠=7±16 J mol-1K-1; k-2=0.164±0.076 s-1; ΔH-2≠=47.0±18.1 kJ mol-1; ΔS-2≠=-101±61 J mol-1 K-1; and k-1/k2=5.90±0.18. The reaction of [PtMe3(OOCH)(bipy)] with NaSCN: k1 =33.5±0.2 s-1; ΔH1≠=58.0±0.4 kJ mol-1; ΔS1≠=-20.5±1.6 J mol-1 K-1; k-2=0.222±0.083 s-1; ΔH-2≠=54.9±6.3 kJ mol-1; ΔS-2≠=-73.0±21.3 J mol-1 K-1; and k-1/k2=12.0±0.3. Conditional pseudo-first-order rate constant k0 increased linearly with the concentration of NaY, while it decreased drastically with the concentration of NaX. Some plausible mechanisms were examined, and the following mechanism was proposed. [Note to reader: Please see article pdf to view this scheme.] © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 523-532, 1998
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Notes: Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with 1-hexanol, 1-methoxy-2-propanol, 2-butoxyethanol, 1,2-ethanediol, and 1,2-propanediol at 296±2 K, of (in units of 10-12 cm3 molecule-1 s-1): 15.8±3.5; 20.9±3.1; 29.4±4.3; 14.7±2.6; and 21.5±4.0, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. These OH radical reaction rate constants are higher than certain of the literature values, by up to a factor of 2. Rate constants were also measured for the reactions of 1-methoxy-2-propanol and 2-butoxyethanol with NO3 radicals and O3, with respective NO3 radical and O3 reaction rate constants (in cm3 molecule-1 s-1 units) of: 1-methoxy-2-propanol, (1.7±0.7)×10-15, and 〈1.1×10-19; and 2-butoxyethanol, (3.0±1.2)×10-15, and 〈1.1×10-19. The dominant tropospheric loss process for the alcohols, glycols, and glycol ethers studied here is calculated to be by reaction with the OH radical, with lifetimes of 0.4-0.8 day for a 24 h average OH radical concentration of 1.0×106 molecule cm-3. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 533-540, 1998
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Notes: Experiments have been carried out on the oxidation of CF3CFH2 (HFC-134a). Reaction was initiated by continuous photolysis of F2 in the near-ultraviolet. The F atoms produced abstracted a hydrogen atom from CF3CFH2 initiating oxidation in gas mixtures containing O2 and made up to a total pressure of 700 torr with N2. Product yields were measured using Fourier-transform infrared (FTIR) spectroscopy. Experiments were performed with several different partial pressures of O2 present, and at three temperatures; 298, 323, and 357 K. The major products were HC(O)F, CF3C(O)F, and CF3O3CF3, consistent with H atom abstraction by O2 and CC bond scission being the dominant loss processes for CF3CFHO radicals:\documentclass{article}\pagestyle{empty}\begin{document}$CF3CFHO+O2 \rightarrow CF3C(O)F+HO2 (4a)$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$CF3CFHO+M \rightarrow CF3+HC(O)F+M (4b)$\end{document}The following expression was derived for the ratio of rate constants for these reactions:k4a/k4b=(3.8±1.6)×10-24 exp[(2400±500)/T]cm3 molecule-1 (viii)The main fate of the CF3 radicals was formation of CF3O3CF3 and small amounts of CF3OH were detected. The results of the present experiments in which F atoms were used to initiate reaction are in good agreement with those of previous studies in which Cl atoms were employed to initiate the oxidation of HFC-134a. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 541-554, 1998
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Notes: Laser-flash photolysis of RBr/O3/SF6/He mixtures at 248 nm has been coupled with BrO detection by time-resolved UV absorption spectroscopy to measure BrO product yields from O(1D) reactions with HBr, CF3Br, CH3Br, CF2ClBr, and CF2HBr at 298±3 K. The measured yields are: HBr, 0.20±0.04; CF3Br, 0.49±0.07; CH3Br, 0.44±0.05; CF2ClBr, 0.31±0.06; and CF2HBr, 0.39±0.07 (uncertainties are 2σ and include estimates of both random and systematic errors). The results are discussed in light of other available information or O(1D)+RBr reactions. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 555-563, 1998
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Notes: In a stirred batch reactor, the Ce(III)- or Mn(II)-catalyzed Belousov-Zhabotinsky reaction with mixed organic acid/ketone substrates exhibits oscillatory behavior. The organic acids studied here are: dl-mandelic acid (MDA), dl-4-bromomandelic acid (BMDA), and dl-4-hydroxymandelic acid (HMDA), and the ketones are: acetone (Me2CO), methyl ethyl ketone (MeCOEt), diethyl ketone (Et2CO), acetophenone (MeCOPh), and cyclohexanone ((CH2)5CO). The effects of bromate ion, organic acid, ketone, metal-ion catalyst, and sulfuric acid concentrations on the oscillatory patterns are investigated. Both conventional and stopped-flow methods are applied to study the kinetics of the oxidation reactions of the above organic acids by Ce(IV) or Mn(III) ion. The order of relative reactivities of the oxidation reactions of organic acids in 1 M H2SO4 is Mn(III)(SINGLEBOND)HMDA reaction 〉 Ce(IV)(SINGLEBOND)HMDA reaction 〉 Mn(III)(SINGLEBOND)BMDA, reaction 〉 Mn(III)(SINGLEBOND)MDA reaction 〉 Ce(IV)(SINGLEBOND)BMDA reaction 〉 Ce(IV)(SINGLEBOND)MDA reaction. Spectrophotometric study of the bromination reactions of the above ketones shows that these reactions are zero-order with respect to bromine and first-order with respect to ketone and that ketone enolization is the rate-determining step. The order of relative rates of bromination or enolization reactions of ketones in 1 M H2SO4 is (CH2)5CO≫(MeCOEt, Et2CO, Me2CO)〉MeCOPh. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet:30: 595-604, 1998
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Notes: The kinetics of the oxidation of diazepam (DZ) by Chloramine-B (CAB) has been studied in aqueous hydrochloric acid medium. The oxidation reaction follows the rate law:\documentclass{article}\pagestyle{empty}\begin{document}$\it{-d[\rm{CAB}]\over\it dt_{\ .}}=k\rm{[CAB][DZ]^{0.6}[HCl]^{0.6}}$\end{document}The dependence of the reaction rate on temperature is studied and activation parameters for the rate-determining step are evaluated. The dielectric constant of the medium has a small effect on the rate. Ionic strength and the reaction product benzenesulfonamide have no effect on the reaction rate. The solvent isotope effect is studied. A probable mechanism for the observed kinetic data is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 605-611, 1998
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Notes: The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [AuIII] as well as [GA]. Both H+ and Cl- ions retard the rate of reaction. AuCl4-, AuCl3(OH2), and AuCl3(OH)- are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613-619, 1998
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Notes: 1,1,1-Trifluoroethane has been decomposed in comparative rate single-pulse shock-tube experiments. The rate expression for elimination at ca. 2.5 bar and in the temperature range of 1050 to 1200 K has been found to be\documentclass{article}\pagestyle{empty}\begin{document}$\it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=7.0\times 10^{14}\ exp(-37260/T)s^{-1}$\end{document}The experimental conditions appear to be such that the unimolecular reaction is at the beginning of the fall-off region and we find that for step sizes down between 500 and 1000 cm-1 the high-pressure rate expression is in the range\documentclass{article}\pagestyle{empty}\begin{document}$\it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=2.0\times 10^{15}\ exp(-38300/T)\ to\ 4\ \times\ 10^{15}\ exp(-39000/T)s^{-1}$\end{document}where the smaller rate parameters refer to the larger step size down. The results are compared with those from an earlier study and the anomalously high A-factor is noted. It is suggested that the existing rate expressions for the fluorinated ethanes may need to be reevaluated. © 1998 John Wiley & Sons, Inc., Int J Chem Kinet: 30: 621-628, 1998
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Notes: This article describes an experimental and modeling study of the oxidation of isobutene. The low-temperature oxidation was studied in a continuous-flow stirred-tank reactor operated at constant temperature (from 833 to 913 K) and pressure (1 atm), with fuel equivalence ratios from 3 to 6 and space times ranging from 1 to 10 s corresponding to isobutene conversion yields from 1 to 50%. The main carbon containing products were analyzed by gas chromatography. The ignition delays of isobutene-oxygen-argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1930 K and pressures from 9.5 to 10.5 atm.A mechanism has been proposed to reproduce the profiles obtained for the reactants consumption and the products formation during the slow oxidation and to compute the ignition delays in the shock tube. Simulations were performed using CHEMKIN II. A correct agreement between the simulated values and the experimental data has been obtained in both apparatuses. The main reaction paths have been determined for both series of measurements by a sensitivity and rate of production analysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 629-640, 1998
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Notes: The authors present a critical analysis of the use of an overall single reaction rate equation instead of the true rate equations corresponding to the decomposition of a substance according to two parallel reactions. Isothermal as well as nonisothermal decomposition are considered. An apparent compensation effect has been evidenced in both cases. It has been assigned to the dependence of the kinetic parameters on temperature (for the isothermal case), conversion, and heating rate (for nonisothermal one). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 673-681, 1998
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Notes: The addition of bromide ions to the component solutions of the Briggs- Rauscher oscillating system produces a variety of phenomena, depending on the sequence of the addition and on the initial bromide concentration. If the addition is made some minutes after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations last for five or six cycles, then suddenly ceases. If the addition is made immediately after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations do not start at all. The addition of bromide ions to an actively oscillating BR reaction causes a rapid suppression of the oscillations. Our observations may be accounted for by a mechanism involving the IBr species. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 641-646, 1998
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Notes: The mechanism of the thermal decomposition of smithsonite has been determined from a comparison of the results obtained from isothermal, linear heating rate (TG), and Constant Rate Thermal Analysis (CRTA) experiments. Two important precautions have been taken in this work. Firstly, the chemical composition of the sample has been checked in order to be sure that pure anhydrous zinc carbonate has been used. Secondly, the experimental conditions have been selected in such a way to avoid the influence of heat and mass transfer phenomena on the forward reaction. It has been shown that the mechanism for the thermal decomposition of smithsonite depends upon temperature. Thus, at temperatures lower than 650 K, approximately, an A0.5 kinetic model describes the reaction, whereas, at temperatures roughly higher than 690 K the above reaction obeys a F1 kinetic law. An interpretation of this behavior is given. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 647-655, 1998
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Notes: Isobutane pyrolysis has been studied in the presence of oxygen at about 773 K in unpacked and in PbO-coated packed Pyrex reactors. The reaction is shown to be accelerated by oxygen in reactors of low surface-to-volume ratio and strongly inhibited in packed PbO-coated reactors. These oxygen effects are explained in terms of interaction between two radical chain systems, one of pyrolysis, the other of oxidation. Oxygen introduces additional chain initiations and a degenerate chain branching step due to H2O2 while oxygenated radicals are efficiently removed at the reactor wall. All experimental results have been modeled and many rate constants of elementary steps were evaluated. The collision efficiency of HO2 radicals on a PbO-coated Pyrex surface has been determined in the temperature range of this study. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 657-671, 1998
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Notes: An experimental and theoretical study of the pyrolysis and oxidation of parabenzoquinone has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 600-1500 K. The main variables considered are temperature, oxygen concentration, and presence of CO. A detailed reaction mechanism for the pyrolysis and oxidation chemistry of parabenzoquinone is proposed, which provides a good description of the experimental results. Both the experimental work and the kinetic mechanism proposed for the pyrolysis and oxidation of parabenzoquinone represent the first systematic study carried out for this important aromatic compound.Our pyrolysis results confirm that the primary dissociation channel for p-benzoquinone leads to CO and a C5H4O isomer, presumably cyclopentadienone. However, significant formation of CO2 during the pyrolysis may indicate the existence of a secondary dissociation channel leading to CO2 and a C5H4 isomer. Under oxidizing conditions, consumption of p-benzoquinone occurs mainly by dissociation at lower temperatures. As the temperature increases interaction of OC6H4O with the radical pool becomes more significant, occurring primarily through hydrogen abstraction reactions followed by ring opening reactions of the OC6H3O radical. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 683-697, 1998
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Notes: The gas-phase reaction of ozone with a series of unsaturated oxygenates and with 1-pentene has been studied at ambient T (287-296 K) and p=1 atm. of air. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 0.22±0.05 for 2 (5H)-furanone, 1.08±0.20 for methacrolein, 1.74±0.20 for crotonaldehyde, 5.84±0.39 for methylvinyl ketone, 1.05±0.15 for methyl acrylate, 3.20±0.47 for vinyl acetate, 59.0±8.7 for cis-3-hexenyl acetate, 154±30 for ethylvinyl ether, ≥(315±23) for linalool, and 10.9±1.4 for 1-pentene. The results are compared to literature data for the compounds studied and for other unsaturated oxygenates, and are discussed in terms of reactivity toward ozone as a function of the nature, number, and position of the oxygen-containing substituents (SINGLEBOND)CHO, (SINGLEBOND)C(O)R, (SINGLEBOND)C(O)OR, and (SINGLEBOND)OC(O)R. Atmospheric implications are briefly examined. © 1998 John Wiley & Sons, Inc. Int. J Chem Kinet: 30: 21-29, 1998.
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Notes: A new linear regression method is applied to determine the rate constants from time-dependent profiles. The method is effective for obtaining the rate constants of such consecutive processes as vibrational relaxation. The ambiguity of ordinary nonlinear analysis is eliminated by the linearization of regression equations. Because the new method also determines relative detectivity, the nascent vibrational distributions immediately following reactions or photolysis can be obtained simultaneously. In order to demonstrate the reliability of the new method under practical conditions, several examples of analysis of the data with noise are shown in detail. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 47-54, 1998.
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Notes: Tartaric acid oxidation by vanadium(V) in sulfuric acid medium was investigated spectrophotometrically at 760 nm and 30°C by appearance of the vanadium(IV), as vanadyl. The reaction rate was determined under pseudo-first-order conditions with an excess of hydroxyacid over the oxidant concentration. The oxidation showed a first-order dependence with respect to vanadium(V) concentration and fractional orders with respect to tartaric acid and sulfuric acid concentrations, with no control and with constant ionic strength. The reaction rate is enhanced by an increase of ionic strength, and slightly reduced by a decrease of the dielectric constant of the medium. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 55-61, 1998.
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Notes: Data relative to methane trapping of SiCl2 and a rate constant for the SiCl2 into C(SINGLEBOND)H bond insertion process of k-1=13.4 M-1s-1 at 921 K are reported. Results on the decomposition of the trapping product, methyldichlorosilane, are also reported. This decomposition follows first-order kinetics with a rate constant of k=1.5±0.2×10-3 s-1 at 905 K and produces methane, trichlorosilane, methyltrichlorosilane, and tetrachlorosilane. It is argued that the decomposition involves silylene intermediates, is nonchain, and is initiated primarily by the molecular methane elimination process MeSiHCl2(SINGLEBOND)1→ CH4+SiCl2. Free radicals and Si(SINGLEBOND)C bond fission may also contribute to the decomposition but are not dominant. The kinetics of MeSiHCl2 decomposition are shown to be consistent with the kinetics of the reverse SiCl2/CH4 trapping reaction and with the overall reaction thermochemistry. Reaction modeling gives product yields, reactant conversions, and rates in reasonable agreement with the data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 89-97, 1998.
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Notes: Kinetic studies of the oxidation of the bis[1-hydroxy-2-(salicylideneamino)ethane]manganese(II) complex by hydrogen peroxide in acetonitrile solutions, at (30.0±0.2)°C, are described. A first-order dependence on the total manganese and the peroxide concentrations was verified, leading to the rapid formation of a Mn(III) intermediate, monitored by stopped-flow measurements, at 394 nm, with a rate constant kf=(1.15±0.03)×105 mol-1 dm3 s-1. The participation of hydroxyl radicals in the process was detected by spin-trapping EPR spectra. The final product was monitored both by EPR spectra, and spectrophotometrically by the slow decay of the intermediary Mn(III) species, with a rate constant kd=(2.60±0.09) s-1. It was identified as the corresponding mononuclear Mn(IV) complex, and characterized by different spectroscopic techniques. Comparative results of the reactivity of the starting complex versus molecular oxygen, leading to the same final product, were also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 889-897, 1998
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Notes: The stoichiometry of CO2 production during the ceric oxidation of various organic acids is measured under conditions with organic acid excess. Measurements utilize a photometric methodology. For anaerobic conditions stoichiometries [CO2]produced:[Ce(IV)]reduced of about 0 (malonic acid), 0.5 (e.g., glyoxylic acid), and 1.0 (oxalic acid) are found. Oxalic acid showed an oxygen-induced decrease of CO2 production, while other compounds such as malonic acid increased the amount of produced CO2 or showed no changes (e.g., tartronic acid). In the case of mesoxalic acid the stoichiometry is increased from about 0.5 to 2.0 due to the presence of molecular oxygen. The results are discussed on the basis of simple reaction mechanisms demonstrating that useful information on reaction pathways and intermediates can be extracted from these simple measurements. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 899-902, 1998
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Notes: The rate constant of the title reaction is determined during thermal decomposition of di-n-pentyl peroxide C5H11O(—)OC5H11 in oxygen over the temperature range 463-523 K. The pyrolysis of di-n-pentyl peroxide in O2/N2 mixtures is studied at atmospheric pressure in passivated quartz vessels. The reaction products are sampled through a micro-probe, collected on a liquid-nitrogen trap and solubilized in liquid acetonitrile. Analysis of the main compound, peroxide C5H10O3, was carried out by GC/MS, GC/MS/MS [electron impact EI and NH3 chemical ionization CI conditions]. After micro-preparative GC separation of this peroxide, the structure of two cyclic isomers (3S*,6S*)3α-hydroxy-6-methyl-1,2-dioxane and (3R*,6S*)3α-hydroxy-6-methyl-1,2-dioxane was determined from 1H NMR spectra. The hydroperoxy-pentanal OHC(—)(CH2)2(—)CH(OOH)(—)CH3 is formed in the gas phase and is in equilibrium with these two cyclic epimers, which are predominant in the liquid phase at room temperature. This peroxide is produced by successive reactions of the n-pentoxy radical: a first one generates the CH3C·H(CH2)3OH radical which reacts with O2 to form CH3CH(OO·)(CH2)3OH; this hydroxyperoxy radical isomerizes and forms the hydroperoxy HOC·H(CH2)2CH(OOH)CH3 radical. This last species leads to the pentanal-hydroperoxide (also called oxo-hydroperoxide, or carbonyl-hydroperoxide, or hydroperoxypentanal), by the reaction HOC·H(CH2)2CH(OOH)CH3+O2→O(=)CH(CH2)2CH(OOH)CH3+HO2.The isomerization rate constant HOCH2CH2CH2CH(OO·)CH3→HOC·HCH2CH2CH(OOH)CH3 (k3) has been determined by comparison to the competing well-known reaction RO2+NO→RO+NO2 (k7). By adding small amounts of NO (0-1.6×1015 molecules cm-3) to the di-n-pentyl peroxide/O2/N2 mixtures, the pentanal-hydroperoxide concentration was decreased, due to the consumption of RO2 radicals by reaction (7). The pentanal-hydroperoxide concentration was measured vs. NO concentration at ten temperatures (463-523 K). The isomerization rate constant involving the H atoms of the CH2(—)OH group was deduced:\documentclass{article}\pagestyle{empty}\begin{document}$k_{3}\rm =(6.4\pm 0.6)\times 10^{10}\hbox{exp}\{-(16,900\pm 700)\hbox{cal mol}^{-1}/RT\}s^{-1}$\end{document}or per H atom:\documentclass{article}\pagestyle{empty}\begin{document}$k_{3\rm (H)}\rm =(3.2\pm 0.3)\times 10^{10}\hbox{exp}\{-(16,900\pm 700)\hbox{cal mol}^{-1}/RT\}s^{-1}$\end{document}The comparison of this rate constant to thermokinetics estimations leads to the conclusion that the strain energy barrier of a seven-member ring transition state is low and near that of a six-member ring. Intramolecular hydroperoxy isomerization reactions produce carbonyl-hydroperoxides which (through atmospheric decomposition) increase concentration of radicals and consequently increase atmospheric pollution, especially tropospheric ozone, during summer anticyclonic periods. Therefore, hydrocarbons used in summer should contain only short chains (〈C4) hydrocarbons or totally branched hydrocarbons, for which isomerization reactions are unlikely. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 875-887, 1998
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Notes: Diffuse Interface Model (DIM) is introduced to describe the mechanism of high-temperature corrosion/internal oxidation. The zone has dissolved oxygen and metal atoms diffuse and react resulting in the inward movement of zone. The high-temperature oxidation data for cobalt, iron, and nickel, which are for metal deficit (p-type), have been analyzed using a nonlinear optimization method to obtain the optimal values for different parameters, diffusivity of metal atoms in metal oxide, diffiusivity of gaseous species in the corrosion product, diffusivity of oxidant in the unreacted solid (metal or alloy), the rate constant for the reaction and the fraction of the zone reacted. The expression for diffusivity in the reaction zone has been modified by relating diffusivities of the product layer and the core as function of fraction of zone reacted. The model was applied to the experimental data for the high-temperature oxidation of cobalt, iron, and nickel by pure oxygen at an atmospheric pressure. The model predicts the values of diffusion coefficients, preexponential factors, and activation energies for diffusion process, which are generally compared favorably with those reported in the literature. Linear relationship are derived relating the diffusion coefficient in the core and product layer to the parabolic rate constant which is valid for iron, cobalt, and nickel for high-temperature oxidation (900-1350°C) by oxygen at an atmospheric pressure according to the following equations:\scriptfont4=\seveni \scriptscriptfont4=\fivei $$D_{\rm P}=1.4\times 10^{-8}\ \it k_{g}$$ $$D_{\rm C}=6.9\times 10^{-9}\ \it k_{g}$$The results of the model have been successfully used to predict the experimentally determined parabolic rate constants for the oxidation of cobalt at high temperatures for two different investigators [6,7] under similar conditions. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 903-912, 1998
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Notes: Rate constants for the reaction of ozone with methylvinyl ketone (H2C(DOUBLEBOND)CHC(O)CH3), methacrolein (H2C(DOUBLEBOND)C(CH3)CHO), methacrylic acid (H2C(DOUBLEBOND)C(CH3)C(O)OH), and acrylic acid (H2C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm3 molecule-1 s-1): methylvinyl ketone (5.4±0.6)×10-18; methacrolein (1.3±0.14)×10-18; methacrylic acid (4.1±0.4)×10-18; and acrylic acid (0.65±0.13)×10-18. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769-776, 1998
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Notes: Nine amino acids, aspartic acid, glycine, serine, tyrosine, alanine, glutamic acid, threonine, cystine, phenylalanine, and two peptides, and two peptides, glycine-glycine peptide, glutamic acid-cystine-glycine peptide, give rise to damped oscillations of the Belousov-Zhabotinskii(BZ) type in a batch reactor. Both Mn2+ and Fe(phen)32 are essential for most of those oscillations; and the oscillations in [Mn3+] and [Fe(phen)33+] are also observed. The role of two metallic ions played in the oscillations are analyzed, showing that Mn2+ catalyzes the oxidation of the amino acids or peptides by BrO3- to produce some intermediates which effectively reduce Br2 to Br- catalyzed by Fe(phen)32+. © 1998 John Wiley & Sons, Inc. Int. J. Chem Kinet 30: 243-247, 1998.
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Notes: Cationic micelles of cetyltrimethylammonium bromide, CTABr, speed attack of hydroxide ion upon coumarin by a factor of c.a-2, due to a concentration effect. The first-order rate constants, kobs, at a given hydroxide ions concentration go through maxima with increasing surfactant concentration. The overall micellar effects in these cationic micelles can be treated in terms of the pseudo-phase ion exchange model. Analysis of the data shows that second-order rate constant at the micellar surface is smaller than the second-order rate constant in water. Anionic micelles of sodium dodecyi sulfate, SDS, inhibit the same reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 273-276, 1998.
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Notes: The kinetics and mechanisms of the reactions of aluminium(III) with pentane-2,4-dione (Hpd), 1,1,1-trifluoro pentane-2,4-dione (Htfpd) and heptane-3,5-dione (Hhptd) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm-3 sodium perchlorate. The kinetic data are consistent with a mechanism in which aluminium(III) reacts with the β-diketones by two pathways, one of which is acid independent while the second exhibits a second-order inverse-acid dependence. The acid-independent pathway is ascribed to a mechanism in which [Al(H2O)6]3+ reacts with the enol tautomers of Hpd, Htfpd, and Hhptd with rate constants of 1.7(±1.3)×10-2, 0.79(±0.21), and 7.5(±1.6)×10-3 dm3 mol-1 s-1, respectively. The inverse acid pathway is consistent with a mechanism in which [Al(H2O)5(OH)]2+ reacts with the enolate ions of Hpd, Htfpd, and Hhptd with rate constants of 4.32(±0.18)×106, 5.84(±0.24)×103, and 1.67(±0.05)×107 dm3 mol-1 s-1, respectively. An alternative formulation involves a pathway in which [Al(H2O)4(OH)2]+ reacts with the protonated enol tautomers of the ligands. This gives rate constants of 2.79(±0.12)×104, 3.86(±0.16)×105, and 8.98(±0.25)×103 dm3 mol-1 s-1 for reaction with Hpd, Htfpd, and Hhptd, respectively. Consideration of the kinetic data reported here together with data from the literature, suggest that [Al(H2O)5(OH)]2+ reacts by an associative or associative-interchange mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 257-266, 1998.
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Notes: The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: kobs=a+b[H+]. The oxidation of [1,1,2,2-2H4]ethanediol exhibited a primary kinetic isotope effect (kH/k D=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 285-290, 1998.
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Notes: No abstract.
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Notes: The effects of mixed CH3CN(SINGLEBOND)H2O solvents on rates of aminolysis of ionized phenyl salicylate, PS-, reveal a nonlinear decrease in the nucleophilic second-order rate constants, knms, (for aminolysis) with increase in the content of CH3CN until it becomes ∼50%, v/v. The values of knms remain almost unchanged with change in the CH3CN content within 50 to 70 or 80%, v/v. The effects of mixed CH3CN(SINGLEBOND)H2O solvents on pKa of leaving group, phenol, and protonated amine nucleophile have been concluded to be the major source for the observed mixed solvent effects on knms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 301-307, 1998.
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Notes: The rate coefficients for the reactions CHFO+F, CFO+F and the self-reaction of CFO were determined over the temperature range of 222-298 K. A computer controlled discharge-flow system with mass spectrometric detection was used. The results are expressed in the Arrhenius form (with energies in J):CHFO+F→CFO+HF:k1(T)=(9.7±0.7)·10-12 exp[-(5940±150)/RT] cm3 molecule-1 s-1CFO+F+M→CF2O+M:FORMULA DISC=“MATH”〉k2(T)=(2.60±1.17)·10-10 exp[-(10110±1250)/RT cm3 molecule-1 s-1FORMULACFO+CFO→CF2O+CO:k3(T)=(3.77±2.7)·10-10 exp[-(8350±2800)/RT] cm3 molecule-1 s-1© 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 329-333, 1998
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Notes: Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H2SO4, HClO4, and CH3COOH by monitoring the formation of Cr(III)-oxalic acid complex at 560 nm. The effect of total [oxalic acid], [Cr(VI)], [H2SO4], [HClO4], and [CH3COOH] on the reaction rate was determined at 30°C. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH3COOH] while it decreases with [H2SO4], [HClO4], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is rate=k1 Kes1 [oxalic acid]T [Cr(VI)]T 1+Kes1 [oxalic acid]T, where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)(SINGLEBOND)oxalic acid 1:1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1:1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C(SINGLEBOND)C bond in the 1:2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 335-340, 1998
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Notes: The thermal dehydrochlorination CF2ClCH3→CF2(DOUBLEBOND)CH2+HCl has been studied in a static system between 597 and 664 K in the presence of CCl4, C2Cl6, CF2(DOUBLEBOND)CH2, HCl, and CF3CH3. A kinetic radical and molecular reaction model has been developed. In addition to describing earlier results on the acceleration of the pyrolysis by CCl4 and the further acceleration by HCl, this model describes quantitatively up to conversions of 20% (i) the dependence of the catalytic effect of CCl4 at low concentrations, (ii) the stronger catalytic effect of C2Cl6, and (iii) the inhibitory effect of added CF2CH2 and CF3CH3 when CCl4 is used as a catalyst. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 359-366, 1998
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Notes: Vacuum line kinetic studies of the reaction of p-toluenesulfonyl chloride and benzene or toluene, using aluminum chloride as the catalyst and dichloromethane as the solvent were determined at 25°C by means of gas chromatography. The reaction is first-order in arene, tosyl chloride, and in AlCl3 as catalyst. Noncompetitive results are kT/kB=22±7 with a product sulfone isomer distribution: ortho, 14±1%; meta, 4.3±0.2%; and para 82±1%. With hexadeuteriobenzene kH/kD was determined to be 1.8±0.1. Rate constant ratios and product isomer distributions were also determined competitively: with AlCl3, kT/kB=30±2; % ortho, 13±1; % meta, 4.0±0.5; % para, 84±3; with SbCl5, kT/kB=40±4; % ortho 10.3±0.4; % meta, 4.7±0.2; and % para, 85.0±0.5. The kT/kB ratio for AlCl3 and the meta sulfone product percentages for both AlCl3 and SbCl5 are considerably higher than those reported in the literature. NMR and Raman studies suggest a molecular complex between p-tosyl chloride and AlCl3, with coordination through oxygen as the dominant species and the probable electrophile in CH2Cl2. A reaction mechanism consistent with the kinetic and spectroscopic results is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 367-372,1998
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Notes: The investigation of high-pressure autoignition of combustible mixtures is of importance in providing both practical information in the design of combustion systems and fundamental measurements to verify and develop chemical kinetic models. The autoignition characteristics of hydrogen-oxygen mixtures at low pressures have been explored extensively, whereas few measurements have been made at high pressures. The present measurements extend the range of pressures up to 4 MPa, where few measurements have yet been reported.Using a rapid compression machine equipped with a specially designed piston head, hydrogen autoignition pressure traces were measured at pressures above the second explosion limit (p=0.6-4 MPa, T=950-1050 K). The measured pressure records show a more gradual pressure increase during induction time in this regime than in the low-pressure regime, indicating that the energy release becomes significant at conditions over the second explosion limit.By comparing the measurements and a thermodynamic model which incorporates the heat transfer and energy release, a modified reaction rate constant for H2O2+H=HO2+H2, one of the most important reactions for hydrogen oxidation at high pressure, and the reaction with the largest uncertainty, is suggested in this work as k17=2.3 . 1013exp(-4000/T) cm3/mol-s. The modeled pressure history with the modified reaction rate agrees well with the measured values during the induction period over the range of conditions tested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 385-406, 1998
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Notes: The kinetics of the substitution reactions of Fe(CN)5H2O3- ion with a series of nitrogen and sulfur containing heterocycles were studied in aqueous media. In the presence of excess ligand, varied over a large range of concentrations, second-order rate constants were calculated at μ = 0.100 M NaClO4. Activation parameters for the formation reactions were found, ΔH*ast; and ΔS*, 28 ± 6 kJ/mol and 135±20 J/mol, respectively. The results are interpreted as being consistent with dissociative, SN1 mechanism. The kinetics of formation and dissociation were studied by stopped-flow technique at several temperatures. An investigation of the kinetics of exchange of coordinated heterocycles for 1,3,5-triazine, yielded rate saturation that is typical of a limiting SN1 mechanism. Activation parameters of the limiting first-order specific rate of dissociations were found with ΔH* and ΔS* 53±2 kJ/mol and 105±5 J/mol, respectively. From the specific rates of formation and dissociation reactions the equilibrium constants were calculated. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 415-418, 1998
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Notes: Manganese(III) solutions were prepared by known electrochemical methods in sulfuric acid, acetic acid, and pyrophosphate media. The nature of the oxidizing species present in manganese(III) solutions was characterized by spectrophotometric and redox potential measurements. Kinetics of oxidation of L-glutamine by manganese(III) in sulfuric acid (1.5 M), acetic acid (60% v/v), and pyrophosphate (pH=1.3) media at 313 K, 323 K, and 328 K, respectively, have been studied. Three different rate laws have been obtained for the three media. Effects of varying ionic strength, solvent composition, and added anions, such as fluoride, chloride, perchlorate, pyrophosphate, and bisulfate, have been investigated. There is evidence for the existence of free radicals as transient species. Activation parameters have been evaluated using Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 7-19, 1998.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: We have examined the kinetics and mechanism of the dediazoniation reaction of p-methylbenzenediazonium tetrafluoroborate in the presence and absence of CuCl2 using a methodology developed by us that allows, simultaneously, and within the same experiment to identify, to quantify, and to obtain the rate constants for the formation of all dediazoniation products, and, indirectly, the rate constant for the diazonium salt decomposition. The methodology developed combines the use of coupling reactions, to form a stable azo dye, followed by analysis by HPLC. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 31-39, 1998.
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Heats of formation of BrONO2, BrONO, BrOOH, FOOH, FOOCl, CF3C(O)OOH, HC(O)OOH, CH3C(O)OOH, and [CH3C(O)O]2 are estimated from bond contributions taken from J. Phys. Chem.,100, 10150 (1996). They agree within ±2 kcal/mol with recent experimental or ab initio data. The resulting BDE(O(SINGLEBOND)O)=36 kcal/mol value in diacetyl peroxide requires the concerted assistance of exothermic C(SINGLEBOND)C(O) weakening in the transition state of its decomposition into free radicals. It also implies the existence of a previously unrecognized 12 kcal/mol nonbonded repulsion in acyl anhydrides. The formation of chloryl chlorate with ΔHf(O2ClOClO2)=50 kcal/mol, a marginally stable species toward dissociation into (ClO3+OClO), may account for observations made in the [O(3P+OClO] system at low temperatures. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 41-45, 1998.
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066